Perform AAAA check separately

[crishoj]

Dependent on the resolver, combined DNS checks for A + AAAA + MX may fail with SERVFAIL, despite valid A/MX records being present.

Case in point: eripio.xyz on Ubuntu 20.04.6 LTS with systemd-resolve (and 1.1.1.1 + 8.8.8.8 as upstream resolvers):

---

This pull request implements the workaround proposed by @sandermarechal in #301:

I have the exact same problem. AAAA validation fails because it gets back a SERVFAIL and dns_get_record() returns FALSE, even though an MX record and A record exist.

Perhaps you should not query MX + A + AAAA at the same time.

[rGaillard]

@crishoj @egulias thank you for this fix! :)